This invention relates generally to shut-off valves used for fluid flow control in low pressure applications. The present invention is particularly useful in fishing vessels such as bass fishing boats, and may be used to drain live wells, such as those described in U.S. Pat. No. 4,708,084 to Campau.
Shut-off valves that are presently used to drain live wells suffer from several drawbacks. Metallic valves, which are typically ball valves, have corrosion problems customarily found in a marine environment. A substantial actuation force is required to close the valve because of friction between the ball and the valve seat. The longer the ball sits, the greater the friction with the seat becomes, and thus the greater the actuation force necessary to unseat the ball.
An attempt to solve this problem has been made by using a plastic ball in the valve. The use of the ball valve still has inherent shortcomings, however. For example, the ball valve is typically actuated by a cable whose force must operate through a stroke of 90.degree., with minimum mechanical advantage at the ends of the stroke, where frictional resistance is greatest. The frictional resistance increases over time as the ball compresses the soft seat. This often leads to break-away forces which may be 10 or more times the force required to move the valve once the "stiction" force is overcome.
To compensate for the higher actuation force and to minimize the control cable strength and stiffness requirements, the valve ports are often made smaller than desirable, to reduce the force necessart to move the ball. This restricts flow through the valve, significantly reducing the drain rate in livewell applications and leads to increased chance of clogging by debris in the livewell water.
Another problem is that ball valves, or gate valves that would be similarly used, required precision manufacturing. The more precise the manufacturing operation is, the more expensive the item becomes.